Telephone system



Patented Apr. 10, 1934 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Horace Edgar Humphries, London, England, assignor to Siemens Brothers & Company Limited, London, England 4 Claims.

This invention relates to automatic and semiautomatic telephone systems and more particularly to improved impulse repeating arrangements for use in connection with inter ofiice working.

In certain known arrangements impulse repetition is effected over a split circuit in which the impulses are repeated from the incoming to the outgoing side of a transmission bridge by means of an impulse accepting relay in the incoming side having contacts included in a loop circuit in the outgoing sideof the circuit. The outgoing side of the circuit usually includes a comparatively high impedance, such as an answering supervisory relay or impedance coils, or both, the high impedance being shunted out of the impulsing circuit by means of contacts of a slow acting relay operated by the first impulse of an impulse train. The first impulse break however, is usually repeated before the slow acting relay operates to shunt the high impedance and as a consequence the energy stored in the impedance dissipates itself through the impulse accepting relay and may cause its false operation and the consequent clipping or mutilation of the first impulse. Also in certain known arrangements the impulse repeating contacts are shunted by contacts of an answering supervisory relay to avoid the outgoing: loop being momentarily opened when the direction of current in the trunk line Wires is reversed in response to the reply of the called subscriber. Further, when two remote circuits are tied together, such as two tandem repeaters, and the impulse repeating contacts in the first are shunted in the manner described, there is a possibility of the called circuit being picked up before it has released since the called circuit remains held during the release of its release relay at the time the originating circuit is free.

As regards impulse repetition, according to the main feature of the present invention a shunt path of lower impedance than the path offered through the impulse accepting relay is connected to the impedance at the commencement of the first impulse of an impulse train and before or substantially at the same time as the outgoing loop circuit to the distant exchange is opened. Therefore upon the opening of the loop to the break portion of the first impulse the energy stored in the impedance will dissipate itself through the low impedance path, the impulse accepting relay being unaffected.

The low'impedance path may be closed over a contact set of the impulse accepting relay, the

contacts being of the make before break type and on relapsing connect the shunt circuit before breaking the loop. An ordinary break before make type of contact may suflice.

The shunt circuit may comprise a short circuit, or a simple non-inductive resistance may be used so that the dissipation of the stored energy occurs gradually which prevents sparking at the impulse repeating contacts.

By the use of make before break impulse repeating contacts, the trouble caused through the possible relapse of the impulse accepting relay on the reversal of line conditions when the called party replies is overcome as the contacts would not open to a momentary flick of the impulse j' accepting relay or if they do open the answering supervisory relay is slow to release by reason of the shunt. Similarly by the omission of shunting contacts across the impulse repeating contacts the calling and distant circuits are released almost simultaneously thus avoiding the possibility of one circuit testing free while the other is held.

The accompanying drawing illustrates by way of example the application of the invention to a simple impulse repeater employing booster battery metering and in which the incoming and outgoing sides are split by condensers, the incoming side being fed with battery over the impulse accepting relay.

The positive, negative and private wires incoming from a selector are marked and P, the positive and negative wires being connected via condensers to outgoing wires 11 and b.

The impulse accepting relay A is bridged across the and wires via make before break change over contacts of a relay DD which is a relief relay to the shunt field answering supervisory relay D bridged across the wires a and b in series with inductance coil I. A make before break change over contact of relay A is included in the wire I), the contact when normal connecting a resistance R across the local exchange side of the wires a and b. Relay B is a usual slow to release release relay and relay C is operative in response to the first impulse of a train to connect a clean impulsing loop to the distant office. Relay J is slow in operation and operated on the seizure of the circuit to prepare for the application of metering conditions. Relays B, C and J being slow to release remain operated throughout trains of impulses.

Considering the circuit in detail, the free condition of the circuit is characterizedby an open wire P, and when a searching selector seizes the circuit relay A operates to a loop condition over the and wires. At contact a1 a circuit is closed for relay J via contact b4, and at contact (12 the impulsing loop to the junction is prepared.

Relay J operates and prepares a locking circuit for itself at contact 7'1. Relay B is operated over contacts 7'2 and a1, and at contact 7'3 an earth is connected to the wire P to busy the repeater against other searching selectors and hold the connection back to the calling party.

At contact b1 earth is prepared for connection to the wire P to busy the repeater when relay J releases, whilst at contact b2 an energizing circuit is closed for the polarizing coil of shunt field relay D. Contact b3 prepares the circuit for relay C, and contact 114 closes a locking circuit for relay B independent of contact 7'2. At contact b the locking circuit for relay J is closed, and at contact 126 the loop to the distant exchange is closed over inductance coil I and upper coil of relay D which relay however does not operate as the currents through its coils are not in the requisite directions to allow the relay to operate.

The circuit is now in a condition to receive impulses.

At the break portion of the first impulse relay A relapses and at contact (11 operates relay C. At contact a2 before relay D and inductance coil I are short circuited by the operation of relay 0 a shunt circuit is connected across the conductors a and I) over resistance R, the eventual breaking of the contact transmitting the break portion of the first impulse over the outgoing junction.

On the breaking of the impulsing loop at contact a2 two circuits are made for the dissipation of the energy stored in inductance coil I and upper coil of relay D, one circuit being through the resistance R and the other through the splitting condensers and relay A. The former circuit is of much lower impedance than the latter with a consequence that the energy will mainly dissipate itself through this circuit leaving relay A unaffected.

Shortly after contact a1 relapses relay 0 operates and at contact 02 closes a short circuit across inductance coil I and relay D, and prepares a clean impulsing loop to the junction. At contact 01 the relapse of relays J and B is guarded against by preparing to earth wire P.

The remaining impulses of the train are transmitted to the outgoing junction over contacts a2, 02 and b6, and after the train has ceased and relay A is held permanently, relay 0 releases to disconnect the non-inductive loop at contact 02 and disconnect the guarding earth from wire P, at contact 01.

When the called party answers the direction of current over the a and b wires is reversed and relay D operates. At contact d1 a circuit is closed for relay DD which relay at contacts ddl and (i012 reverses the battery connections to the and wires. At contact (M3 the busy earth is disconnected and a booster battery connected to the wire P over the wire BB to cause the operation of the calling partys meter.

The circuit for relay J is broken at contact d124, but this relay being slow to release does not release immediately but allows ample time for the metering signal to be passed over wire P. However on the relapse of relay J the booster battery is removed and an earth over contact b1 connected. At contacts '1 and 7'2 the locking circuit for relay J and the temporary locking circuit for relay B, respectively are broken.

During the change over of contacts ddl and (1112 on the operation of relay D and DD it is probable that a momentary release of relay A will occur, the release however will generally be of such short duration that the contacts a2, being make before break, will not relapse to break the outgoing loop. If the contacts a2 do fully relapse the resistance R will be placed across the upper coil of relay D, in efiect making this relay slow to release, the relay holding up until relay A re-operates. The momentary opening of the loop to the junction will not affect the apparatus at the distant end as the release relay in this circuit will remain operated during the short opening of the line.

It will be clearly seen that if the shunt circuit is not provided the only path through which the energy may dissipate is through the splitting condensers and relay A which relay may operate and clip the impulse.

When the calling party releases relay A relapses opening the circuit of relay B at contact (11, relay B releases in turn opening the circuit for relays D and DD. Almost simultaneously with the restoration of contact a1, a2 restores and disconnects the loop to the distant exchange. Thus the release relays at the home and distant exchanges commence to restore almost simultaneously, the release of both circuits occurring almost at the same time thus neither circuit will be held whilst the other is free.

The contact a2 may be of the ordinary break before make change over type, but the characteristics of the contact must be such that the break on relapse occurs very late and just prior to the make, so that the discharge from the impedance does not flow for a suificient period before the shunt R is connected by the make to cause the operation of relay A. Further the resistance R is not necessary as a simple short circuit will sufiice, but however the inclusion of a resistance in the shunt circuit is preferred as this prevents sparking across the impulse repeating contacts when relay A relapses.

What I claim as new and desire to secure by Letters Patent is:

1. In an impulse repeater, a line relay in bridge of the line incoming to said repeater, a supervisory relay in bridge of the line on the outgoing side, contacts on the line relay for closing the outgoing line when the line relay energizes, and contacts on the line relay closed by deenergization thereof for shunting the supervisory relay.

2. In an impulse repeater, a line relay in bridge of the incoming line, an impedance in bridge of the outgoing line, contacts on the line relay for closing the outgoing line circuit through said impedance, thereby magnetizing the same, and meansoperated by the line relay on deenergizing to break said outgoing line circuit which is effective to dissipate the energy stored in the said impedance and thus prevent such energy from interfering with the proper operation of the line relay.

3. In an impulse repeater, a line relay in bridge of the incoming line, an impedance in bridge of the outgoing line, contacts on the line relay for closing the outgoing line in series with the said impedance when the line relay is energized, a relay for shunting said impedance, a circuit closed through said shunting relay by deenergization of the line relay responsive to incuit when the line relay deenergizes, an impedance in the outgoing line circuit at the repeater, and means for shunting said impedance upon deenergization of the line relay, said means being effective before the outgoing line circuit is opened.

HORACE EDGAR HUMPHRIES. 

